1. Technical Field
The present invention relates to a light source control device and a projector.
2. Related Art
Solid-state light source such as laser diodes (LD) or light emitting diodes (LED) have advantages such as low power consumption, long life, small amount of heat generation, possibility of downsizing, and easiness of lighting/extinction control compared to halogen lamps or high-pressure mercury lamps. Therefore, in recent years, the solid-state light sources have been fast becoming to be used in a variety of fields. For example, in the projectors for displaying images on the screen, the solid-state light sources have started to be actively used for the purpose mainly of reducing the power consumption and the amount of heat generation to thereby achieve downsizing and weight reduction.
If the solid-state light sources such as LD or LED are deteriorated, the light intensity obtained tends to be degraded even if the current supplied thereto does not vary. In general, it is important for the light sources to provide constant light intensity irrespectively of the variation in the environmental temperature and the level of the deterioration. Therefore, in the past, it has been arranged that in the case in which the drop of the light intensity due to the deterioration of the solid-state light source has occurred, the supply amount of the current to the solid-state light source has been increased to thereby obtain a constant light intensity. It should be noted that there is a possibility that the deterioration of the solid-state light source is promoted due to the heat generation if the supply amount of the current to the solid-state light source is increased excessively.
JP-A-2005-32798 discloses a technology of detecting the drive current supplied to the LD, and then generating an error detection signal when the current value exceeds a predetermined value to perform, for example, output stoppage on the drive current to the LD, thereby preventing the deterioration and failure of the drive device for driving the LD from occurring. Further, JP-A-2002-329924 discloses a technology of detecting and storing the current value output from the LD drive device, obtaining the variation in the current value between the detected current value at present and the current value stored in advance to determine whether or not the deterioration of the LD is reaching the terminal stage, thereby making it possible to replace the LD before the fatal deterioration of the LD occurs.
Incidentally, as typical control methods of the solid-state light source, there can be cited the constant current control and the constant power control. The constant current control is a control method of performing the control so as to supply the solid-state light source with a constant current. In contrast, the constant power control is a control method of performing the control so as to supply the solid-state light source with a constant power. Since the light with the light intensity corresponding to the current supplied thereto is emitted from the solid-state light source, the constant current control, with which the light intensity is easily controlled, is often used. The constant power control is used in the case in which the power consumption is made constant, for example.
Here, in the case in which a light intensity higher than the intensity of the light emitted from one solid-state light source is required, there is used a light source device provided with a plurality of solid-state light sources arranged in a line or a sheet and connected in series or in parallel. For example, the projector described above is required to provide a light intensity so high as to make it possible to view the image displayed on a screen illuminated with an illumination device such as a fluorescent lamp to some extent, and is therefore almost required to have the light source device provided with a plurality of solid-state light sources arranged.
In such a light source device provided with a plurality of solid-state light sources, there can occur a situation in which some of the plurality of solid-state light sources shorts (short-circuits) due to deterioration to thereby cause the forward voltage drop (Vf) to be lowered rapidly. If the rapid variation in the forward voltage drop occurs during the operation of the constant power control, there arises a problem that an excessive current is supplied in order for making the power constant to cause the deterioration and failure of the other normal solid-state light sources to thereby shorten the life of the light source device. Further, if the rapid variation in the forward voltage drop occurs during the operation of the constant current control, there arises a problem that the light intensity is lowered as much as the light intensity corresponding to the solid-state light sources shorted to thereby cause light intensity variation although the excessive current supply can be avoided.